Data Sheet

Hartcran House, 231 Kenton Lane, Harrow, Middlesex, HA3 8RP, England
Tel: +44 (0) 20 8909 9595, Fax: +44 (0) 20 8909 2233,
Issue 1, 26 June 2014
868MHz band Narrow Band FM sub-miniature TX
The MTX3 transmitter module adds a totally new
sub-miniature form factor to the existing range of
Radiometrix ISM band devices. Using cutting
edge integrated RF devices, it offers multi
channel, low power narrowband operation in a
previously unobtainable size. It is ideally suited
to applications where existing wideband
modules have insufficient range and where
physically be too big to fit in.
Figure 1: MTX3-869-10-SAL
Conforms to EN 300 220-2 and EN 301 489-3
High performance Fractional N (Sigma-Delta) Synthesizer with TCXO
Vibration resistant (negligible microphony)
Data rates up to 10 kbps for standard module
Usable range over 500m (with suitable aerials and matching receiver)
Fully screened. Very low profile
Feature-rich interface (analogue and digital baseband)
Re-programmable via RS232 interface
Low power requirements
Keyfobs and other hand held terminals
Small form factor data loggers
Industrial telemetry and telecommand
In-building environmental monitoring and control
Covert, high-end security devices
Unobtrusive fire alarm sensors
Heavy vehicle/machinery controls
Technical Summary
Operating frequency:
869.2125 and 869.2375MHz (Social alarms)
(Design will cover 850 - 880MHz)
915MHz band version available
Other custom UHF bands
850-950MHz version (MTX3) also available
4 parallel channels (also fully controllable via serial port)
Transmit power: +10dBm (10mW)
Supply range: 3.1 – 15V (will operate down to 2.9V)
Current consumption: 24mA @ 10mW
Data bit rate: 10kbps max. (standard module)
Serial configuration by inverted RS232 at 3V CMOS level
Size: 23 x 12.5 x 7 mm
Evaluation platforms: NBEK + matching carrier board
Radiometrix Ltd
MTX3 Data Sheet
page 1
Figure 2: MTX3 block diagram
Radiometrix Ltd
MTX3 Data Sheet
page 2
Figure 3: MTX3 footpint (top view)
Pin description – MTX3
RF output (to antenna)
2.9V – 15V DC power supply (@ 10mW)
Transmit Enable (active high)
Serial frequency programming / configuration
DC coupled input for 3V CMOS logic. Rin=47kΩ
Parallel Channel select
Parallel Channel select LSB
1. Serial programming is by the application of a logic level inverted RS232 datastream at 9600 baud to
the EN/PGM pin. The unit must be fully enabled (5mS after the rising edge of the EN signal) before a
programming burst can be properly decoded.
2. Channel select inputs have pull-ups (50kΩ) to 3V internal rail. Do not exceed 3V logic levels on this
port. Do not drive pins high when unit is turned off
3. Channel select inputs are active low. If unused, allow them to remain unconnected
4. EN has a 100kΩ pulldown resistor
5. All pins are on a 2mm grid
6. In the 'off' state there are no transmit state spurii
7. The unit will operate (with marginally reduced specifications and lower (6-8mW) output power) from
a 2.9 – 3.0V rail. This must be well regulated and without noise or ripple, as in this state the unit's
internal regulator no longer operates, and provides no supply rejection.
8. Switching time as controlled by the EN pin is <5ms, but when power is first applied to the unit there
is a 20ms long “calibration” period before the transmitter becomes active
Radiometrix Ltd
MTX3 Data Sheet
page 3
Condensed specifications
Frequency stability
Channel spacing
Number of channels
Operating temperature
Spurious radiations
Output power
Peak deviation
TX on switching time
Modulation type
TX modulation bandwidth
Adjacent channel TX power
TX spurious
Recommended PCB hole size
Radiometrix Ltd
Social alarms: 869.2125 and 869.2375MHz (design will cover
915MHz band version available
25kHz, 20KHz
4 channels controlled by parallel port, or 256 sequential,
or direct control of PLL device via RS232 interface
-20 ºC to +70 ºC (Storage -30 ºC to +70 ºC)
Compliant with ETSI EN 300 220-3 and EN 301 489-3
+10dBm (10mW) ±1dB
5mW/7dBm version available
5ms from EN transition
DC – 5kHz (3V CMOS compatible)
<-45dBm (no RF output in Standby)
3.1V – 15V (usable down to 2.9v)
24mA @ 10mW (nominal)
<3µA standby (EN low or floating)
data (CMOS/TTL compatible)
23 x 12.5 x 7mm
6 pin, 2mm pitch header
2pin 2mm pitch header
MTX3 Data Sheet
page 4
Channel Programming
It is useful at this point to describe how an MTX3 defines it's operating frequency:
At the heart of the device is a fractional N synthesizer locked to a high stability VCXO. The minimum step
size of this PLL is (approximately) 24.8Hz
The data required by the PLL consists of two coefficients: the integer and the fraction. Output frequency
relates to these values thus:
Output frequency (in MHz) = 13 x (integer + (fraction / 2^19))
For correct operation, the component (fraction / 2^19) must have a value between 1 and 2 (in other words,
the "fraction" coefficient varies between 524288 and 1048576) while the value of "integer" is limited by the
operating frequency range of the device (850 to 890MHz) so will lie between 64 and 79
So how do you calculate it by hand ?
Take the frequency, divide it by 13
Take the whole number part remaining, subtract one from it, and that's "integer"
Take everything right of the decimal point, add one and multiply by 524288, and that's "fraction"
Example: 869MHz divide by 13 equals 66.84615384
Subtract one from whole number, i.e. 66 –1
so "integer" = 65
and fraction = (0. 84615384 +1) x 524288 = 967916
and to confirm: 13 x (65+(967916/524288)) does indeed equal 869MHz (minus 7.6Hz)
In interface terms, these coefficients are expressed as a 32 bit binary word (eight hexadecimal digits) where
the most significant byte comprises the integer value, and the remaining three bytes (24 bits) make up
When programming the MTX3, keep in mind that the unit maintains (in RAM) the current values of all
programmable values (current frequency, band of operation, RF power and frequency offset adjustments
and the sequential table values) and that toggling the EN pin does NOT erase or corrupt them.
These values are only loaded from eeprom at cold start power-up (but not when the EN pin is cycled) or
when the unit is commanded to execute eeprom reads by certain serial functions (such as the
"@PRG_00000000" command)
There are no (or very few) "write a value to eeprom" commands. It is usually necessary to load the relevant
current operating RAM value(s) and THEN issue a suitable command to write the RAM value to eeprom.
The MTX3 eeprom stores a set of frequency coefficients for each parallel channel plus a fifth set for the
sequential table start. It also stores power level, frequency offset, sequential table step size and sequential
channel, and the band select constant
Programming a value or coefficient over the serial bus over-writes the previous value and implements this
change on the PLL immediately, but does not change the eeprom contents until a relevant "program eeprom"
command is issued
In general, the most recent stimulus received by the unit will decide the operating frequency and mode
(although if sequential mode has been selected (serial channel not equal to zero) a change to the parallel
port or a direct frequency program command will not initiate a frequency change).
Radiometrix Ltd
MTX3 Data Sheet
page 5
Operation Modes
The MTX3 has three different modes of operation:
1. Parallel. By default the MTX3 operates on one of the four channels selected by the parallel input pins. At
power up, or when a change of parallel input is detected, the current frequency coefficients are loaded from
the eeprom stores corresponding to parallel channels 0-3. The parallel input consists of an inverted 2 bit
binary number applied to P0/P1 (often from a 2 pole switch)
2. Sequential. If a (sequential) channel is programmed over the serial port, the unit sets it's operating
frequency according to this channel number, the programmed table start frequency and the currently
programmed table step size. If the channel is set to zero, the unit returns to default parallel operation.
If the (sequential) channel is programmed into eeprom, the unit will default to this channel at power up
The table can be considered to be a 255 entry table, starting at channel 1, with the frequency incrementing
by the programmed step size for each increment in channel number (it can be seen that, if a 256 entry table
starting with channel zero is desired then programming all the parallel channels to the ch0 frequency, and
the sequential table start value to ch1 will achieve this)
3. Direct. Whenever a frequency coefficient is programmed into the unit, the frequency will change
immediately to this new value regardless of other modes or operation. This is the simplest and most flexible
means of controlling the unit.
If a unit is set in sequential table mode (ie: channel value isn't zero), then direct programming cannot be
used to over-ride the selected channel (executing an @PRG_iiffffff will just set up a set of frequency
coefficients ready to be written to rom. It won't change the actual operating frequency)
Serial interface commands
MTX3 serial interface consists of an inverted RS232 datastream (9600 baud, 1+8+1, no parity) applied to the
EN pin (the idle state of the interface will turn the transmitter on)
Every command string starts with the phrase "@PRG_"
The characters in a command string must not be separated by more than 5mS (so typing individual
characters on a terminal keyboard will NOT work), but a pause of at least 10mS is required between
commands (more following a BURN_ROM command. In this case a much longer idle period, of 50mS at
least, is needed for eeprom programming)
Frequency setting commands
@PRG_iiffffff <cr>
sets the current (temporary) frequency
iiffffff is an 8 digit hexadecimal number (4 bytes):
ii is the 1 byte "integer" coefficient
ffffff is the 3 byte "fraction" coefficient
Frequency (in MHz) = 13 x integer + 13 x (fraction/2^19)
The component (fraction/2^19) must be in the range 1-2
@PRG_BURN_CH0 <cr>
write current frequency into channel 0 eeprom
@PRG_BURN_CH1 <cr>
write current frequency into channel 1 eeprom
@PRG_BURN_CH2 <cr>
write current frequency into channel 2 eeprom
@PRG_BURN_CH3 <cr>
write current frequency into channel 3 eeprom
(these functions do NOT program band/power/offset values)
Radiometrix Ltd
MTX3 Data Sheet
page 6
Sequential table operations
@PRG_0001zzzz <cr>
program zzzz as the sequential table step size
sets the current frequency coefficients as the sequential table start
frequency and programs this, and the step size, into eeprom
@PRG_000000 cc <cr>
@PRG_0000FF cc <cr>
@PRG_0000AA nn <cr>
set cc as sequential channel number
set cc as above AND program it into eeprom
set a maximum channel limit (nn) for the table
Setting channel to zero disables sequential table operation
Serial port on/off commands
@PRG_POWER 00<cr>
@PRG_00000000 <cr>
will turn the unit completely off
(this command does NOT also zero the power setting variable)
Unit is turned back on
(or by cycling the EN pin)
If the unit is in "software off" it will still decode valid commands (although
an invalid string will be interpreted as an EN pin cycle, and the unit will
turn on).
The parallel port will also be read, although not acted upon until the unit is
will cause the unit to re-set itself to the values currently stored in eeprom
(just like what happens at power-up). This also zeros the stored serial
channel and does a parallel channel read
The characters in a command string must not be separated by more than 5mS, but a pause of at
least 10mS is required between commands (more following a BURN_ROM command a much longer
idle period, of 50mS at least, is needed)
The complete list of the MTX3 commands
@PRG_iiffffff <cr>
@PRG_0001zzzz <cr>
@PRG_00000000 <cr>
@PRG_000000cc <cr>
@PRG_0000FFcc <cr>
@PRG_0000AAnn <cr>
@PRG_BURN_CH0 <cr>
@PRG_BURN_CH1 <cr>
@PRG_BURN_CH2 <cr>
@PRG_BURN_CH3 <cr>
@PRG_POWER pp <cr>
@PRG_TRIM+ aa <cr>
@PRG_TRIM- aa <cr>
@PRG_BAND# bb <cr>
@PRG_POWER 00 <cr>
Radiometrix Ltd
sets the current operating frequency (in RAM)
(ii is never zero, ffffff is in the range 080000 - 0FFFFF)
will program zzzz as the sequential table step size
eeprom values to RAM (cold start-up) and channel = 0
will set cc as sequential channel number (in RAM)
will set cc as above AND program it into eeprom
will set (nn) as maximum channel limit for the table and program it into
write current frequency into channel 0 eeprom
write current frequency into channel 1 eeprom
write current frequency into channel 2 eeprom
write current frequency into channel 3 eeprom
write band, power and offset into eeprom
set table start to current frequency AND write both this and the current
step size values to eeprom
sets power variable
set a positive frequency trim offset
set a negative frequency trim offset
set band divider code (bb is O8,0A,0B or 0D)
turn unit off
turn unit back on
MTX3 Data Sheet
page 7
Antenna considerations and options
The choice and positioning of transmitter and receiver antennas is of the utmost importance and is the single
most significant factor in determining system range. The following notes are intended to assist the user in
choosing the most effective arrangement for a given application.
Nearby conducting objects such as a PCB or battery can cause detuning or screening of the antenna which
severely reduces efficiency. Ideally the antenna should stick out from the top of the product and be entirely in
the clear, however this is often not desirable for practical or ergonomic reasons and a compromise may need
to be reached. If an internal antenna must be used, try to keep it away from other metal components and pay
particular attention to the “hot” end (i.e. the far end), as this is generally the most susceptible to detuning.
The space around the antenna is as important as the antenna itself.
Two types of antenna are recommended for use with the MTX3
Whip (¼-wave): This consists simply of a piece of wire or rod connected to the module at one end. The
lengths given below are from module pin to antenna tip including any interconnecting wire or tracking (but
not including any 50Ω coax or microstrip connection). This antenna is simple, cheap, easy to set up and
performs well. It is especially effective when used with a ground plane, which in practice is often provided by
the main PCB or by a metal case.
Base-loaded whip: In applications where space is at a premium a shortened whip may be used, tuned by
means of a coil inserted at the base. This coil may be air-wound for maximum efficiency, or a small SMT
inductor can be used. The value must be empirically chosen to tune the particular length of whip for best
results “in situ”, making this antenna more difficult to set up. Radiated power will generally be slightly less
than that obtained from a ¼-wave whip.
wire, rod, PCB track
or a combination of these
L (mm) = 71250 / freq(MHz)
shortened wire, rod, PCB track etc.
with loading coil.
SMT inductor may be used if reqd.
1/4-wave whip
Base-loaded whip
Fig. 4: Antenna configurations
Other types of antennas are feasible but tend to have drawbacks at these frequencies. Helical and tuned
loop antennas are both very compact but tricky to set up, and can be impractical at 868MHz because of their
very small size. Microstrip patch antennas are relatively large in area, directional, and have gain.
Note: Where the specified antennas are mounted on the PCB and/or in close proximity to metalwork (module
casing, components, PCB tracking etc), the antenna radiation pattern may be seriously affected. Radiated
power may be significantly increased in some directions (sometimes by as much as 10dB) and
correspondingly reduced in others. This may adversely affect system performance where good all-round
coverage is desired.
Care should also be taken to ensure that this effect does not increase the radiated power in any direction
beyond that allowed by type approval regulations. Where this occurs the antenna may need to be relocated.
In extreme cases a resistive attenuator of appropriate value may be required between the module and
Radiometrix Ltd
MTX3 Data Sheet
page 8
Ordering Information
Standard frequency setup for 4 channel MTX3 radios uses these default channels:
Part no.
CH0: 869.2125, CH1-3: 869.2375MHz (for Social Alarm use)
868 – 870 MHz
868 – 870 MHz (with 5mW RF power)
Alternatively, the MTX3 can be supplied as a single frequency module with factory set channel (like the
NTX3B or similar unit). In this case all channels are supplied programmed to the same frequency.
Part no.
CH0 - 3: 869.2125MHz
CH0 - 3: 869.2375MHz
Note: Also available on the other UHF band frequencies, including 915MHz or 433 (MTX2)
Matching COR3 receiver
Part no.
Radiometrix Ltd
CH0: 869.2125, CH13: 869.2375MHz
CH0: 869.2125, CH13: 869.2375MHz
Module mounting
Vertical Mounting,
Parallel pins
Horizontal Mounting,
Perpendicular pins
Vertical Mounting,
Parallel pins
MTX3 Data Sheet
AF, RXD, P3, P2, P1, P0/PGM
page 9
Radiometrix Ltd
Hartcran House
231 Kenton Lane
Harrow, Middlesex
Tel: +44 (0) 20 8909 9595
Fax: +44 (0) 20 8909 2233
[email protected]
Copyright notice
This product data sheet is the original work and copyrighted property of Radiometrix Ltd. Reproduction in
whole or in part must give clear acknowledgement to the copyright owner.
Limitation of liability
The information furnished by Radiometrix Ltd is believed to be accurate and reliable. Radiometrix Ltd
reserves the right to make changes or improvements in the design, specification or manufacture of its
subassembly products without notice. Radiometrix Ltd does not assume any liability arising from the
application or use of any product or circuit described herein, nor for any infringements of patents or other
rights of third parties which may result from the use of its products. This data sheet neither states nor
implies warranty of any kind, including fitness for any particular application. These radio devices may be
subject to radio interference and may not function as intended if interference is present. We do NOT
recommend their use for life critical applications.
The Intrastat commodity code for all our modules is: 8542 6000.
R&TTE Directive
After 7 April 2001 the manufacturer can only place finished product on the market under the provisions of
the R&TTE Directive. Equipment within the scope of the R&TTE Directive may demonstrate compliance
to the essential requirements specified in Article 3 of the Directive, as appropriate to the particular
Further details are available on The Office of Communications (Ofcom) web site:
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Tel: +44 (0)845 456 3000 or 020 7981 3040
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[email protected]
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Tel. +45 33896300
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